Split mojo_system dylib into public and private

mojo/system/simple_dispatcher.h

Index: mojo/system/simple_dispatcher.h
diff --git a/mojo/system/simple_dispatcher.h b/mojo/system/simple_dispatcher.h
index 4ef37d1d10427be7c92216d33b94477a9c0919b2..0ad49ac7d156d668b91722357f889b7bb8170141 100644
--- a/mojo/system/simple_dispatcher.h
+++ b/mojo/system/simple_dispatcher.h
@@ -8,8 +8,8 @@
 #include <list>
 
 #include "base/basictypes.h"
-#include "mojo/public/system/system_export.h"
 #include "mojo/system/dispatcher.h"
+#include "mojo/system/system_impl_export.h"
 #include "mojo/system/waiter_list.h"
 
 namespace mojo {
@@ -19,7 +19,7 @@ namespace system {
 // correspondence between handles and dispatchers (see the explanatory comment
 // in core_impl.cc). This class implements the standard waiter-signalling
 // mechanism in that case.
-class MOJO_SYSTEM_EXPORT SimpleDispatcher : public Dispatcher {
+class MOJO_SYSTEM_IMPL_EXPORT SimpleDispatcher : public Dispatcher {
  protected:
   SimpleDispatcher();